“Improving rearing efficiency of large bluegill by reducing
social costs and enhancing feed quality”

Advisor: Dr. Robert S.
Hayward

Existing culture
technology for bluegills (Lepomismacrochirus) requires more than two years of pond
rearing to produce them within the prevailing food-market size range of
227-340 g, which seems to be less or no profitable to fish producers in the
Midwest U.S. Recent work at MU demonstrated that male bluegills have
substantially greater growth capacity than females when they were reared in
isolated chambers. However, predominantly male bluegill groups did not
differ from mixed sex groups in growth performance when reared in indoor
system. It was recently identified that formation of social hierarchy enabled
only fewer dominant fish increasing access to feed which eventually caused
poor feed and growth efficiency, both in mixed-sex and predominantly-male
groups. My work will involve ameliorating
adverse social interactions among bluegills and thereby allowing them to
grow at rates closer to their inherent capacity in indoor rearing systems.
I try to accomplish this goal by evaluating

(i) the effects of physical structures on growth and social
hierarchy of juvenile bluegills - an approach via reducing visual
encounters

(ii) the effectiveness of a “topping-off” approach to
increase production of food-size bluegills via sequential removal of
dominant fish

Unlike indoor system
where bluegills are grown under high rearing density and with artificial
feed, pond system provides natural shelters, and natural feed, which may wane
the interference competition. It may be possible that prolonged rearing
allows establishment social hierarchy and impedes inherent growth capacity.
My objective is to evaluate
potential to grow higher number of bluegills to food-market size more
readily in ponds, by rearing predominantly male bluegill groups and
reducing social costs, if present.

Whilst social costs
impeding the rearing efficiency, excess fat accumulation have been observed
in the visceral organs at least for the dominant bluegills in the group. It
was identified that farmers, because of absence of specific feed, use other
commercial diets such as those developed for trout and catfish. Feeding
bluegills with non-specific diets led to problems such as increased feed
cost and fat deposition. Social hierarchy and non-specific feed (eg. trout feed), together, questioned the profitability
and long term survivability of the farming because of the increased operational
costs. My goal in this part is to develop
a suitable practical diet for juvenile and adult bluegills by optimizing
amino acid and energy requirements. This study will involve determining

(i) apparent digestibility values of common feedstuffs for
bluegill using individual test ingredients